The long term objectives of this grant proposal are to allow the applicant to develop into an independent physician scientist. In this proposal we present 3 synergistic mechanisms towards that end. 1) Research plan; The applicant proposes to study the regulation of Th17/Th1 responses in the animal model of collagen induced arthritis. This will be addressed in 3 specific aims: Specific Aim 1: To study the changes in Thi7 and Thi responses associated with onset and severity of arthritis following administration of lL-4DCs; Specific Aim 2 and 3: To understand the regulation of Thi 7 and Thi responses by costimulatory molecules in collagen induced arthritis 2) Formal didactic training: the applicant will enroll in immunobiology courses as well as attend seminars and national meetings. 3) Advisory committee: the applicant has formed an advisory committee to not only provide guidance during this process, but also evaluate her progress towards an independent physician scientist. The applicants training will happen at the University of Arizona, Tucson, Arizona. RELEVANCE (See instructions): Rheumatoid arthritis is associated with pain, swelling, deformity of the hands and feet. The prevalence remains at 1%. A significant proportion of patients do not benefit from the existing therapeutic options. This proposal is focused on identifying and understanding another cytokine, lL-17, that may have a pathogenic role in rheumatoid arthritis.